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[[Image:carbonyl-general.png|150px|thumb|right|Carbonyl group]]

==Overview==
In [[organic chemistry]], a '''carbonyl group''' is a [[functional group]] composed of a [[carbon]] [[atom]] [[double bond|double-bonded]] to an [[oxygen]] atom : C=O. 

The term carbonyl can also refer to [[carbon monoxide]] as a [[ligand]] in an [[inorganic]] or [[organometallic]] complex (a [[metal carbonyl]], e.g. [[nickel carbonyl]]); in this situation, carbon is [[triple-bonded]] to oxygen : C≡O. 

The remainder of this article concerns itself with the [[organic chemistry]] definition of '''carbonyl'''.

==Carbonyl compounds==

A carbonyl group characterizes the following types of compounds (where -CO denotes a C=O  carbonyl group):

{|class=wikitable
|align=center|'''Compound||[[Aldehyde]]||[[Ketone]]||[[Carboxylic acid]]||[[Ester]]||[[Amide]]||[[Enone]]||[[Acyl chloride]]||[[Acid anhydride]]
|-
|align=center|'''Structure'''||[[Image:Aldehyde2.jpg|60px|Aldehyde]]||[[Image:Ketone-general.png|60px|Ketone]]||[[Image:Carboxylic-acid.svg|60px|Carboxylic acid]]||[[Image:Ester.png|60px|Ester]]||[[Image:Amide-general.png|80px|Amide]]||[[Image:Enone-general.png|90px|Enone]]||[[Image:Acyl-chloride.png|60px|Acyl chloride]]||[[Image:Carboxylic-acid-anhydride.png|95px|Acid anhydride]]
|-
|align=center|'''General formula'''||RCHO||RCOR'||RCOOH||RCOOR'|||<nowiki>RCONR'R''</nowiki>||<nowiki>RC(O)C(R')CR''R'''</nowiki>||RCOCl||(RCO)<sub>2</sub>O
|-
|}

Other organic carbonyls are [[urea]] and [[carbamate]]s. Examples of inorganic carbonyl compounds are [[carbon dioxide]], [[carbonyl sulfide]] and [[phosgene]]

==Reactivity==
'''''Oxygen''''' is more [[electronegative]] than carbon, and thus pulls electron density away from carbon to increase the bond's [[Polarity (physics)|polarity]]. Therefore, the carbonyl carbon becomes [[electrophile|electrophilic]], and thus more reactive with [[nucleophile]]s. Also, the electronegative oxygen can react with an electrophile; for example a proton in an acidic solution or other Lewis Acid.'''

The [[alpha hydrogen]] in a carbonyl compound is much more acidic (~10<sup>30</sup> times more acidic) than a typical CH bond.  For example the pK<sub>a</sub> values of [[acetaldehyde]] and [[acetone]] are 16.7 and 19, respectively.<ref>Ouellette, R.J. and Rawn, J.D. “Organic Chemistry” 1st Ed.  Prentice-Hall, Inc., 1996: New Jersey.  ISBN 0-02-390171-3.</ref>

Amides are the most stable of the carbonyl couplings due to their high resonance stabilization between the Nitrogen-Carbon and Carbon-Oxygen bonds.

Carbonyl groups can be [[redox|reduced]] by reaction with [[hydride]] reagents such as NaBH<sub>4</sub> and LiAlH<sub>4</sub>, and by [[organometallic]] reagents such as [[organolithium]] reagents and [[Grignard reagent]]s. 

Other important reactions include:
* [[Wolff-Kishner reduction]]
* [[Clemmensen reduction]]
* Conversion into [[thioacetal]]s
* [[Hydration]] to [[hemiacetal]]s and [[hemiketal]]s, and then to [[acetal]]s and [[ketal]]s
* Reaction with [[ammonia]] and primary [[amine]]s to form [[imine]]s
* Reaction with [[hydroxylamine]]s to form [[oxime]]s
* Reaction with [[cyanide]] anion to form [[cyanohydrin]]s
* Oxidation with oxaziridines to [[Acyloin#Enolate oxidation by sulfonyloxazirines|acyloin]]s
* Reaction with [[Tebbe's reagent]] and [[phosphonium ylide]]s to [[alkene]]s.
* [[Perkin reaction]]
* [[Tishchenko reaction]]
* [[Aldol condensation]]
* [[Cannizaro's reaction]]

== α,β-Unsaturated carbonyl compounds==
'''α,β-Unsaturated carbonyl compounds''' are an important class of carbonyl compounds with the general structure C<sub>β</sub>=C<sub>α</sub>−C=O. In these compounds the carbonyl group is [[conjugated system|conjugated]] with an [[alkene]] (hence the [[adjective]] [[saturation (chemistry)|unsaturated]]), from which they derive special properties. Examples of unsaturated carbonyls are [[acrolein]], [[mesityl oxide]], [[acrylic acid]] and [[maleic acid]]. Unsaturated carbonyls can be prepared in the laboratory in an [[aldol reaction]] and in the [[Perkin reaction]].
The carbonyl group, be it an [[aldehyde]] or [[acid]], draws electrons away from the alkene and the alkene group in unsaturated carbonyls are therefore deactived towards an [[electrophile]] such as [[bromine]] or [[hydrochloric acid]]. As a general rule with unsymmetric electrophiles hydrogen attaches itself at the α position in an [[electrophilic addition]].  
On the other hand, these compounds are activated towards [[nucleophile]]s in [[nucleophilic addition]].

==Spectroscopy==
*[[Infrared spectroscopy]]: the C=O double bond absorbs [[infrared]] light at [[wavenumber]]s between approximately 1600&ndash;1900 cm<sup>−1</sup>. The exact location of the absorption is well understood with respect to the geometry of the molecule. This absorption is known as the "carbonyl stretch" when displayed on an infrared absorption spectrum.<ref>Mayo D.W., Miller F.A and Hannah R.W “Course Notes On The Interpretation of Infrared and Raman Spectra” 1st Ed.  John Wiley & Sons Inc, 2004: New Jersey.  ISBN 0-471-24823-1.</ref>
*[[Nuclear magnetic resonance]]: the C=O double-bond exhibits different resonances depending on surrounding atoms, generally a downfield shift.  The <sup>13</sup>C NMR of a carbonyl carbon is in the range of 160-220 ppm.

==See also==
*[[Organic chemistry]]

==Further reading==
* L.G. Wade, Jr. ''Organic Chemistry, 5th ed.'' [[Prentice Hall]], 2002. ISBN 0-13-033832-X
* The Frostburg State University Chemistry Department. [http://www.chemhelper.com/ Organic Chemistry Help] (2000).
* Advanced Chemistry Development, Inc. [http://www.acdlabs.com/iupac/nomenclature IUPAC Nomenclature of Organic Chemistry] (1997).
* William Reusch. [http://www.cem.msu.edu/~reusch/VirtualText/intro1.htm VirtualText of Organic Chemistry] (2004).
* Purdue Chemistry Department [http://chemed.chem.purdue.edu/genchem/topicreview/bp/2organic/carbonyl.html] (retrieved Sep 2006).  Includes water solubility data.
* William Reusch. (2004) [http://www.cem.msu.edu/~reusch/VirtualText/aldket1.htm Aldehydes and Ketones] Retrieved 23 May 2005.
* ILPI. (2005) [http://www.ilpi.com/msds/ref/anhydride.html The MSDS Hyperglossary- Anhydride].

==References==
{{reflist|2}}

[[Category:Functional groups]]

[[ca:Carbonil]]
[[cs:Karbonylové sloučeniny]]
[[da:Carbonylgruppe]]
[[de:Carbonylgruppe]]
[[et:Karbonüülrühm]]
[[es:Grupo carbonilo]]
[[eo:Karbonila grupo]]
[[fr:Composé carbonylé]]
[[ko:카보닐기]]
[[it:Carbonile]]
[[he:קרבוניל]]
[[nl:Carbonylgroep]]
[[ja:カルボニル基]]
[[no:Karbonyl]]
[[pl:Grupa karbonylowa]]
[[pt:Carbonila]]
[[ru:Карбонильная группа]]
[[sk:Karbonylová skupina]]
[[tr:Karbonil grubu]]
[[uk:Карбонільна група]]
[[zh:羰基]]

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